The present invention relates to self adjusting friction clutches and friction clutches.
Friction clutches are known which comprise a clutch cover attached to a flywheel with at least one spring acting on a pressure plate to force a driven plate into frictional engagement with the flywheel.
It is also known for friction clutches to have a constant lift device which limits movement of the pressure plate away from the flywheel during disengagement of the clutch to a substantially constant distance throughout the life of the clutch.
It is an object of the present invention to provide an improved form of constant lift device which is more compact than heretofore known constant lift devices, and in particular, more compact in an axial direction when considering the rotational axis of the clutch.
Thus according to the present invention there is provided a self adjusting friction clutch comprising a clutch cover, a pressure plate rotationally fast with the cover but axially displaceable towards a driven plate by spring means so that the driven plate is clamped between the pressure plate and an associated flywheel to engage the clutch, an adjustment device to compensate for wear in the clutch, at least part of the adjustment device being located in the force path between the spring means and the pressure plate, and at least one constant lift device to limit lift of the pressure plate during clutch disengagement such that the bias force of the spring means acting on the adjustment device is reduced when the clutch is substantially fully disengaged to assist operation of the adjustment device, characterised in that the or each constant lift device comprises a lever pivotally connected to one of the pressure plate or an axially fixed component of the clutch and which lever during disengagement of the clutch contacts, at a point remote from the pivot, an abutment on the other of the pressure plate or the axially fixed component to limit lift of the pressure plate, and means to control the angular position of the lever with respect to the said one of the pressure plate or the axially fixed component to maintain the lift of the pressure plate substantially constant over the life of the clutch, the adjustment device and the constant lift device thus co-operating to maintain the clamp load of the spring means substantially constant as the clutch wears.
According to a further aspect of the present invention there is provided a friction clutch comprising a cover attached to a flywheel with at least one spring capable of acting to bias a pressure plate into frictional engagement with a driven plate, the driven plate in turn being biased into frictional engagement with the flywheel, and at least one constant lift device mounted on one of the pressure plate or an anally fixed component of the clutch, each constant lift device comprising a first abutment for contact with a further abutment on the other of the pressure plate or axially fixed component to limit lift of the pressure plate during clutch disengagement, the position of the first abutment relative to said one of the pressure plate or axially fixed component being adjustable in response to wear of the friction surfaces of the driven plate so as to maintain the lift of the pressure plate during disengagement of the clutch substantially constant, characterized in that the constant lift mechanism comprises a lever pivotally connected to said one of the pressure plate or axially fixed component, the lever carrying the first abutment at a point remote from the pivotal connection, and means to control the angle of the lever, the control means comprising a pin slidable relative to said one of the pressure plate or axially fixed component in response to wear, the arrangement being such that the amount by which the pin slides is different from the corresponding amount of wear of the driven plate
According to a further aspect of the present invention there is provided friction clutch comprising a clutch cover attached to a flywheel with at least one spring means capable of acting to bias a pressure plate into frictional engagement with a driven plate, the driven plate in turn being biased into frictional engagement with the flywheel, and at least one constant lift device acting to limit lift of the pressure plate during clutch disengagement to a substantially constant value and being mounted on one of the pressure plate or an axially fixed component, the or each constant lift device including a pin slidable relative to said one of the pressure plate or axially fixed component to permit adjustment of the constant lift device in response to wear of the friction surfaces of the clutch, characterised in that a force is applied to the pin which is dependent upon the speed of rotation of the clutch, and which force is operative to prevent adjustment of the constant lift device above a predetermined speed of rotation of the clutch.